Abstract

We experimentally and theoretically investigated the rapid solidification and microstructural evolution of freely falling droplets of the ternary Fe45Cu40Co15 peritectic alloy, with the critical undercooling temperature of metastable liquid phase-separation initiation being measured to be 38 K. We found that liquid phase separation occurs when the droplet diameter ranges from 80 to 980 μm, resulting in the formation of either microscopically or macroscopically segregated microstructures. The peritectic solidification microstructure was produced when the droplet diameter either exceeded 980 μm or was below 80 μm. The dispersed morphology of the large alloy droplets possessed nonuniformly dispersive characteristics, i.e., proximity to the droplet surface is negatively associated with the size of Cu-rich globules. With the further reduction of the droplet size, the phase-separated morphology first transformed into a core–shell structure and finally displayed a homogeneously dispersed structure. Our theoretical calculations showed that the residual Stokes motion, Marangoni convection, and surface segregation are the dominant dynamic mechanisms for the phase separation and microstructural evolution under reduced-gravity conditions inside the drop tube.

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Acknowledgments

This study was supported financially by the National Natural Science Foundation of China (Grant Nos. 51671161, 51371150 and 51327901) and the Natural Science Foundation Research Project of Shaanxi Province of China (Grant No. 2017JM5116).